AB0762 DIAGNOSTIC YIELD OF BIOPSIES IN EOSINOPHILIC GRANULOMATOSIS WITH POLYANGIITIS: A SINGLE CENTRE EXPERIENCE
Authors: R. Ríos-Garcés, J. Hernández-Rodríguez, S. Prieto-González, M. C. Cid, G. Espígol-Frigolé
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Recently published classification criteria for eosinophilic granulomatosis with polyangiitis (EGPA) <sup>[1]</sup> require, to be applied, a diagnosis of small- or medium-vessel vasculitis, without specifying how that diagnosis should be made. Histologically, EGPA is characterized by eosinophil-rich and necrotizing granulomatous inflammation together with necrotizing vasculitis, predominantly affecting small to medium vessels. Some of these features are not specific for EGPA and may be seen in other forms of ANCA associated vasculitis (AAV). Current guidelines on the management of AAV recommend biopsies to assist in establishing a new diagnosis and for further evaluation of patients with suspected relapse <sup>[2]</sup>. Therefore, biopsies are essential tools for the diagnosis, classification and management of these diseases. <h3>Objectives</h3> To describe the histopathological findings, diagnostic yield and the most common localizations of biopsies performed to assist in the diagnosis and follow-up of patients with EGPA. <h3>Methods</h3> Medical charts of patients with EGPA regularly followed at our department were reviewed to retrieve the number and localization of biopsies, as well as biopsy findings including proportion of a) eosinophil-rich extravascular inflammation, b) granulomas and/or c) necrotizing vasculitis. Biopsies were performed if patients presented symptoms in any given and most accessible localization (at diagnosis) or if they were necessary to confirm active disease (during follow-up). <h3>Results</h3> Among 59 EGPA patients regularly controlled at our department, a total of 163 biopsies were performed on 54 of them. In 44 patients (81.5%), 89 biopsies were performed at diagnosis and in 27 (50%), 74 biopsies were performed during follow-up. A total of 37 biopsies in 26 patients (48.1%) had proven vasculitis. A total of 7 biopsies in 5 patients (9.3%) had proven granuloma. A total of 87 biopsies in 42 patients (77.8%) had proven eosinophil-rich extravascular inflammation. The main localizations were: ear, nose and throat (ENT, 49 biopsies), respiratory (31), skin (25), gastrointestinal (GI, 18), muscular (14), nerve (12), bone marrow (8), renal (4) and temporal artery biopsy (TAB, 2). Among them, at least 1 typical histological feature detailed above was found in: ENT 38/49 biopsies (sensitivity of 77.6%), respiratory 15/31 (48.4%), skin 23/25 (92%), GI 10/18 (55.6%), muscular 4/14 (28.6%), nerve 5/12 (41.7%), bone marrow 6/8 (75%), renal 4/4 (100%) and TAB 1/2 (50%). A total of 57 biopsies performed in 29 patients (53.7%) showed none of the typical findings described above, although only 6 patients had all their biopsies without abnormal findings. These results are summarized in Table 1. <h3>Conclusion</h3> Multiple tissues are biopsied in clinical practice to assist in the diagnosis and evaluation of patients with EGPA, according to the multi-organ nature of this disease. Biopsies are more frequently obtained from accessible sites such as ENT or skin and usually dictated by clinical manifestations. In our cohort, the highest sensitivity was obtained from kidney, skin, ENT, bone marrow? and GI tract. <h3>References</h3> [1]Grayson et al, Ann Rheum Dis 2022 [2]Yates et al, Ann Rheum Dis 2016 <h3>Acknowledgements</h3> This study was supported by Instituto de Salud Carlos III (ISCIII) through the project PI18/00461, part of Plan Estatal de Investigación Científica y Técnica y de Innovación 2013–2016, and co-funded by the European Union. Roberto Ríos-Garcés is a recipient of a Río Hortega grant from Instituto de Salud Carlos III, Spain (CM19/00032). <h3>Disclosure of Interests</h3> Roberto Ríos-Garcés: None declared, José Hernández-Rodríguez: None declared, Sergio Prieto-González: None declared, Maria C. Cid Paid instructor for: Vifor, GSK, Consultant of: GSK, Abbvie and Janssen, Grant/research support from: Kiniksa, Georgina Espígol-Frigolé Consultant of: Janssen.